#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 30

void error_handling(char* message);

int main(int argc, char* argv[])
{
    int recv_sock;
    struct sockaddr_in adr;
    struct ip_mreq join_adr;//设置加入多播组的结构体

    int str_len;
    char buf[BUF_SIZE];

    if(argc != 3)
    {
        printf("Usage : %s <group> <ip> \n", argv[0]);
        exit(1);
    }

    recv_sock = socket(PF_INET, SOCK_DGRAM, 0);

    memset(&adr, 0, sizeof(adr));
    adr.sin_family = AF_INET;
    adr.sin_addr.s_addr = htonl(INADDR_ANY);
    adr.sin_port = htons(atoi(argv[2]));

    if(bind(recv_sock, (struct sockaddr*)&adr, sizeof(adr)) == -1)
            error_handling("bind() error\n");

    join_adr.imr_multiaddr.s_addr = inet_addr(argv[1]);//多播组地址信息
    join_adr.imr_interface.s_addr = htonl(INADDR_ANY);//加入多播组的主机地址信息

    setsockopt(recv_sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void*)&join_adr, sizeof(join_adr));

    while(1)
    {
        str_len = recvfrom(recv_sock, buf, BUF_SIZE - 1, 0, NULL, 0);
        if(str_len < 0)
            break;
        buf[str_len] = 0;
        fputs(buf, stdout);
    }
    close(recv_sock);
    return 0;
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(-1);
}
